The removal by theft of movable objects such as bicycles and television sets has been a problem to which considerable attention has been given. In this respect, it is desirable to provide an alarm system which will emit a short warning signal to put persons disturbing the object on notice. Thereafterwards, if the disturbance continues, it is desired to activate the alarm system for emitting a continuous audible alarm system of high intensity. Such an alarm system must be highly reliable and accurate in detecting disturbances whether they be motion disturbances or other disturbance conditions such as fire and smoke. Providing a compact alarm system which can be conveniently installed within the cabinet of a television set, or other like appliance, is also desirable. However, the simplicity and compactness of the system must not sacrifice the reliability of the system in detecting a disturbance and quickly emitting an audible alarm signal.
Prior systems have been developed such as shown in U.S. Pat. No. 3,828,338 wherein an auxiliary buzzer and a main buzzer are provided. The auxiliary buzzer sounds at the first instance of a detected vibration and thereafterwards, when the vibration has occurred a predetermined number of times, as counted by a ring counter, a main buzzer is energized. Both of the buzzers are selectively connected to the power supply through relay switches.
Another alarm system is disclosed in U.S. Pat. No. 3,713,128 wherein the numbers of pulses produced by a disturbance detector are counted and once a predetermined number of counts is reached, a multivibrator is triggered to deliver a pulse to a low frequency pulse counter. When two pulses are received by the multivibrator within a predetermined amount of time, a relay coil is de-energized to actuate the audible alarm signal. However, such systems are rather sophisticated and are mainly suitable for application to stationary structures for detecting disturbances such as the entrance of burglars, or fire and smoke.
U.S. Pat. No. 3,721,956 shows a relatively simple alarm system which is operable by vibration for attachment to a device such as a bicycle. A vibration or motion responsive cantilevered member is contained within a tube and establishes momentary electrical contact with the tube for latching on a silicon control rectifier when the bicycle is moved and the alarm is activated by turning a key switch to an "on" position. Once the alarm is sounded, the alarm remains on until the key is switched "off". No provision is made for sounding a short audible warning signal prior to the continuous operation of the alarm signal so that the person disturbing the object has the option of ceasing his disturbance in which instance the alarm will not be continuously activated.